Why may Puck be considered the protagonist in A Midsummer Night's Dream by William Shakespeare and not Bottom?
A Midsummer Night's Dream by William Shakespeare does not have a traditional protagonist. Normally, a protagonist is both the most important character in a play and the person whose desires, needs, or situation drives the plot of the play. The main conflict of the play is usually concerned with how the protagonist struggles against obstacles to reach a goal or resolve a problem, sometimes successfully and sometimes not.
The main conflicts in the play are among the two sets of young lovers and Titania and Oberon. In the case of the young lovers, we have a fairly conventional narrative trajectory in which Hermia loves Lysander and Helena loves Demetrius but there are obstacles to their happy unions; after a few plot twists, both young women end up with the men they love. Thus in this sense we have a very traditional comic plot arc in the lovers' stories, and in some ways the young lovers are the closest characters to traditional protagonists.
The Titania-Oberon conflict over the changeling is also resolved, but we do not have a fully fleshed out narrative arc, meaning that they do not function as protagonists.
Bottom, as one of the rustics, functions as comic relief, and although he is part of Titania's story, his role, and that of the play within the play, are comic diversions; he has no major narrative of his own about his own aspirations and goals.
Puck is a more important character in the play than Bottom, but carries out his deeds at the behest of Oberon. We don't really get a sense of Puck as having motives and a story of his own, but merely acting in and recounting the stories of others. In a way, he is like the playwright, a creator and facilitator of other people's stories rather than the protagonist in his own story.